I. Field of the Invention
The present invention relates generally to vehicle-mounted concrete mixing and dispensing systems and, more particularly, to on-board auxiliary fluid supply systems employed to supply water for washout or adding water to a concrete mix. Specifically, the present invention relates to a pump-operated on-board auxiliary fluid supply system that eliminates the need for a pressurized tank and is self purging of residual fluid.
II. Related Art
Transit concrete mixing trucks, sometimes referred to as ready-mix trucks, have long been in use. They are equipped with large chassis-mounted rotatable mixing drums for mixing and dispensing a quantity of concrete. The drums typically are mounted on an incline and have an opening in the upper end for receiving ingredients to be mixed and discharging mixed concrete products. Loading is accomplished through a charge hopper which extends a distance into the opening of the drum. The drum is further provided with internal helical flights or fins extending around its internal surface which acts to mix the concrete when the drum is caused to rotate in one direction and cause the concrete to be discharged out of the opening when the rotation of the drum is reversed. The upper portion of the drum includes a ring and roller system for drum support and rotation that is carried by a heavy pedestal support assembly.
After mixing and discharge, such concrete mixing drums retain an amount of residual concrete on the mixing fins and inner drum surface and discharge chutes which needs to be periodically washed out to prevent it from curing and hardening inside the drum and on external chutes. Therefore, it has become part of the operating routine to wash the interior of the drum and the discharge chutes one or more times per day. In addition, it may be necessary to add additional makeup water to a mix in the drum prior to discharge.
In conjunction with the use of makeup or washout water on transit concrete mixing trucks, it has further become a common practice to provide a water supply on the vehicle. The supply has included a water tank that has been typically pressurized to 50 psi or higher by a supply of air from a compressor carried on the truck. This, in turn, supplies water under pressure for washout or other uses through hoses and a valving system in a well-known manner.
Such a prior system is illustrated in FIGS. 1a and 1b in which a concrete mixer truck, generally at 10, having a mixing drum 12 and discharge chute 14 is provided with a pressurizable auxiliary water tank 16 mounted on the vehicle. As seen in FIG. 1b, the auxiliary water tank 16 includes an air inlet valve 20 that controls the flow of air under pressure from a pressure source (not shown) through an air supply line (also not shown). An air pressure regulator with gauge 22 is provided, together with a pressure relief or pop-off valve at 24, which prevents over-pressurization of the system. A discharge outlet pipe or hose is provided at 26 suitably valved at 28. The system may be purged by using pressurized air to clear the hose or pipe 26.
More recently, however, government regulations have curtailed the use of such pressurized tanks in many areas and so it would be desirable to eliminate the need for pressurization of the tank without diminishing the washout or easy purge capabilities of the system.